Ontogenic development of IgE-bearing lymphocytes will be studied in the rat. Cell suspensions of fetal liver, neonatal spleen and bone marrow cells will be examined for surface immunoglobulin by immunofluroescence. Co-existence of IgE and IgM on B cells will be examined by double staining and by capping. Recently, we found that mesenteric lymph node cells from rats infected with Nippostrongylus brasiliensis (Nb) secret soluble factor(s) which generate IgE-bearing lymphocytes in normal bone marrow cell culture. Source of this factor, origin of IgE-bearing cells and mechanisms involved in dfferentiation will be studied. As mesenteric lymph node cells from Nb-infected rats contain IgE-bearing lymphocytes, these cells will be stimulated with Nb-antigen, pokeweed mitogen (PWM) or lipopolysaccharide (LPS) to follow differentiation of IgE-bearing cells to IgE forming cells. Possible participation of T cells in the differentiation will be explored using inbred rats and by mixing B cell rich fractions with T cell-rich fraction from different sources. We anticipate that lymph node cells from Nb-infected animals may release T cell factor(s) for IgE upon stimulation with Nb-antigen. Using IgE-bearing cells generated from normal bone marrow cells in vitro, role of T cell factors in the differentiation of IgE-bearing cells to IgE-forming cells will be studied.